We have a rather self-centred, but understandable concern that we and other organisms in our ecosystem may fall victim to the presence of toxic substances in our environment. We fear contact in the air we breathe, the water we drink and the food we eat. We try to avoid exposure to them by buying "organic" foods and persuading reluctant government agencies to "get tough" with polluters. But let's step back for a moment and look at this situation from the viewpoint of a molecule of toxic substance such as DDT. If it could record its biography, it might read something like this.

March 1984. Was sprayed as part of 100 grams of DDT on to the walls of a house in Mexico to kill mosquitoes for malaria control.

July 1984. Evaporated into the room air then escaped to the outdoors. Carried by winds north to Tennessee. Trapped on the needles of a pine tree in the Smokey Mountains, fell with the pine needle to the forest floor and remained there for nearly 10 years.

June 1994. Evaporated again and was carried in the wind north to Lake Superior and was deposited a few days later into the lake by the rain of a thunderstorm. Spent four years in the lake water.

August 1998. Evaporated yet again and continued the journey north to the Arctic near Resolute. Was dumped by an early snowfall into the ocean, only to be drawn into the gills of an arctic cod and absorbed into its fat. Overwintered in the waters of Lancaster Sound trapped in the cod's fat.

July 1999. My host, the cod, was eaten by a seal and I was digested, only to be later transported in milk to a hungry pup. Unfortunately this pup was caught by a polar bear, eaten, and I ended up in the bear's liver.

October 1999. Finally met my end at the age of 15 years in the bear's liver, where I caused some toxicity, but in doing so, my molecular structure was torn apart by its enzymes and I degraded to harmless CO2 water and chloride.

It was Rachel Carson who in 1962 first sounded the alarm in "Silent Spring" that molecules such as DDT could undertake such long journeys reaching unexpected places and causing unexpected effects such as bird-kills. In the nearly four decades since then we have learned a great deal about how molecules such as DDT journey through the environment. We can even predict their fate with some reliability provided that we devote sufficient effort to understanding their properties and the nature of the environments they encounter during their lifetime journey. We also need to monitor the air, water, soils and organisms which provide resting places for these journeying toxics.

Creating an environment free from adverse effects of toxic substances must be based on understanding how all chemicals of commerce (and those produced accidentally) will enter and journey through the environment. We must control or eliminate the release of the substance because once released in the environment it is beyond our control - like leaves in the wind. This task of improving our ability to understand and predict the behaviour of chemicals in the environment is the mandate of the Environmental Modelling Centre at Trent University which was set up in 1995 with industrial, government and university support to devise new and improved predictions in the form of computer calculations or models. These models are now downloaded at a rate of about 7 per day from our web site at www.trentu.ca/envmodel and are widely used by industry and government agencies as well as academics in over 20 countries.

The task is daunting. About 20 million chemicals are known to science. Over 22000 chemicals are used commercially in Canada. Some 500 to 1,000 new chemicals are believed to enter commerce each year. Environment Canada and Health Canada have assessed only about 60 chemicals under the Canadian Environmental Protection Act. Twelve have been banned or restricted by the United National Environmental Program. We have only scratched the surface! What is clearly needed is a concerted international effort to identify the most significant toxic chemicals and regulate them appropriately. It is a challenging task, but we now have much of the know-how to accomplish it.

Canada, as a cold country has a particularly strong stake in this issue. The computer models suggest that, just as frost tends to accumulate in the freezer, toxic chemicals tend to accumulate in cold regions of our planet. Contaminants are better preserved in cold climates because of the lack of microbial activity - the same principle that preserves food in a freezer. Snow is an efficient trap for toxic substances. Those who live in the North tend to eat more locally caught "country foods" rich in fat as distinct from the artificially fed meats, poultry and dairy products which are common in southern supermarkets.

Canada commands some respect internationally because of its success in maintaining a relatively clean and healthful environment. Canadians have been at the forefront of environmental science, especially concerning issues of arctic contamination. But success is breeding complacency. Environmental issues have slipped badly among national priorities. Groups such as the Environmental Modelling Centre at Trent University and its sister groups such as Oliver Ecological Centre at Bobcaygeon have a key role to play by building up a deeper understanding of toxic substances in our complex and changing environment. Only by investing in research, especially by supporting students in environmental science, can we gain the knowledge to ensure that the benefits of chemicals are enjoyed without risk to our health and the diversity of wildlife who share our ecosystem.